In motor vehicles, collision warning systems are becoming more widely used. Collision warning systems provide a vehicle operator knowledge and awareness of objects or vehicles within a close proximity, so as to prevent colliding with those objects. Current collision warning systems usually rely on a sensor located on the vehicle which, upon sensing an object generates an object detection signal, which is communicated to the operator of that vehicle as a warning of a potential collision.
One class of such collision warning system is a rear-end collision warning system. Rear-end collisions may cause so called whiplash injuries to occupants of the vehicle being rear-ended. Thus, there exist today systems for preventing or mitigating whiplash related injuries during rear-end collisions. Such systems usually rely on electric reversible seat-belt retractors or tensioners. One such system is known through WO2008002756, which relates to a control system for warning a following vehicle of a potential collision with a leading vehicle.
In WO2008002756 the leading vehicle is equipped with a rear collision warning system that can determine the range and range rate of the following vehicle using radar sensors or ultrasonic sensors. The control system employs an algorithm that detects the following vehicle and determines whether the potential exists for a collision with the leading vehicle. The algorithm compares a desired distance between the leading vehicle and the following vehicle based on the speed of the leading vehicle, and determines whether the difference between the desired distance and the actual distance is greater than a predetermined threshold. If the difference is greater than the threshold, the algorithm may provide one or more operations, such as flashing hazard lights to warn the following vehicle, or taking other courses of action in the event of an imminent collision, such as pre-tensioning seat belts.
However, it is a well-known fact that many vehicle drivers have a quite aggressive style of driving. Such aggressive driving increases the number of instances when a driver comes close to a rear-end collision. Known systems, as e.g., the system known through WO2008002756, may therefore falsely classify these instances as instances where a collision is imminent.
As a consequence thereof known systems equipped with electric reversible seat-belt retractors or tensioners therefore are often set to activate the retractors or tensioners at a very late instance prior to a rear-end collision, in order to avoid a too frequent activation thereof which may cause a disturbance and be perceived as annoying by vehicle occupants.
However, rear-end collisions between two moving vehicles often occur very rapidly, such that late activation may provide for an insufficient amount of time for such known systems to be able to fully accomplish appropriate positioning of a vehicle occupant in order to effect adequate protection against injuries, such as e.g., whiplash injuries.
Several attempts have been made to ensure that instances of non-threatening driving are not falsely classified as instances where a collision is imminent. One such attempt is illustrated by U.S. Pat. No. 6,758,495, which relates to a method and system for restraining an occupant on a vehicle seat, the occupant being pulled into the vehicle seat is provided with a force by a belt tensioner when a critical driving state is detected and then held in a pulled-back position on the vehicle seat with a holding force. A forward-looking detection system for a dangerous driving state is provided, in which, when a dangerous driving state is detected, a belt tensioner is subjected to a force and the occupant is thereby pulled into the vehicle seat, and in which the occupant is held in a pulled-back position on the vehicle seat.
According to U.S. Pat. No. 6,758,495 a trigger criterion for belt tensioners can thus be derived by determining critical driving situations and/or with the aid of the forward-looking sensor system. The critical vehicle state is detected by monitoring the steering angle, distance from an object, relative velocity, vehicle deceleration, yaw angle, yaw rate, yawing acceleration, vehicle's own speed, steering angle, sharp changes in direction, jump in the road/tire friction coefficient, lateral acceleration, wheel speed and/or angle of inclination or any combination of these parameters. Using the distance from the object, the relative velocity, vehicle's own speed, vehicle deceleration or even the friction coefficient as parameters, for example, a time of collision is determined from this, i.e. the time the electrical reversible belt tensioner has to spare before the time of collision. All the data from detection devices and calculation units or any combination of these data are fed to a control unit, which then compares them with predetermined limiting values and triggers the reversible belt tensioner if these values are exceeded.
Although the method and system suggested by U.S. Pat. No. 6,758,495 may provide for improved classification of driving instances as non-threatening or threatening, there is no provision for ensuring an allowance of a sufficient amount of time to be able to fully accomplish appropriate positioning of a vehicle occupant in order to effect adequate protection against whiplash injuries.